Various attempts have been made to control deactivation of an active material to make the release slow or to change solubility of an active ingredient. For instance, it has been proposed that volatile active materials, such as perfumes, can be modified by adsorption onto a porous substance, conversion to a clathrate compound thereof, entrapping in gel, or the like technique. These techniques do not involve chemical reaction of the active material.
On the other hand, it is known to obtain controlled release of an active material or to change solubility of an active material through chemical modification. For example, there have been proposed a process in which amino groups or carboxyl groups of proteins, such as enzymes, are reacted with a modified polyethylene glycol having a specific structure as disclosed in Japanese Patent Application (OPI) No. 104323/84 (the term "OPI" as used herein means "unexamined published Japanese patent application") and Biochemical and Biophysical Research Communications, Vol. 121, 261-265 (1984) as to reaction of amino groups, and in Japanese Patent Publication No. 7649/83 as to reaction of carboxyl groups; and a process in which amino groups of proteins are reacted with a copolymer having an acid anhydride group, e.g., an olefin-maleic anhydride copolymer, as reported in Macromolecules as Drugs and as Carriers for Biologically Active Materials, 160-181, The New York Academy of Sciences (1985).